The present invention relates to a vehicle brake control device that generates a braking force by moving a piston of a wheel cylinder (hereinafter, referred to as “W/C”) by both a service brake and an electronic parking brake (hereinafter, referred to as “EPB”) generating a hydraulic brake pressure on the basis of a driver's braking operation.
JP-T-2007-519568 discloses a brake system including an electrically-controllable service brake that can generate a braking force independently of a driver's operation and an electrically-controllable EPB that can generate and maintain a braking force.
In the brake system, W/C pressure by the service brake is employed to reduce the power of a motor at the time of operating a parking brake, thereby accomplishing a decrease in size of the EPB. Specifically, in the brake system, a piston of the W/C is moved not only by introducing a hydraulic brake pressure into the W/C by the service brake and but also by moving a driving shaft by driving the motor of the EPB. Accordingly, by moving the piston to a brake pad in advance using the W/C pressure by the service brake at the time of operating the parking brake, it is possible to reduce the power of the motor using the EPB. As a result, it is possible to reduce the size of the motor and thus to reduce the size of the EPB.
In such a brake system, at the time of releasing the W/C pressure by the service brake, the piston is urged to the driving shaft with the releasing of the W/C pressure by the restoring forces of the piston and the brake pad which have been elastically deformed by the W/C pressure. Accordingly, when the releasing of the W/C pressure by the service brake and the contact of the driving shaft, which has been moved by the motor driving of the EPB, with the piston are synchronized with each other, the piston having been urged to the driving shaft with the releasing of the W/C pressure may collide with the driving shaft with a great impact, thereby applying a large load to the driving shaft. In order to endure such an impact, an increase in size of an EPB mechanism such as the driving shaft, the W/C receiving the EPB mechanism, or a caliper body is likely to be necessary.